1. Field of the Invention
The present invention relates to an ultra-directional speaker system and to a method of driving an ultra-directional speaker system, and more specifically it relates to an ultra-direction speaker system that uses ultrasonic waves and provides high directionality and provides an optimum acoustic signal to a location at which a listener exists.
2. Background of the Invention
In the past, there has been a known ultra-directional speaker system that used ultrasonic waves and provided high directionality.
Specifically, in an ultra-directional speaker system that used a parametric speaker system in the past, the existence of a listener in an audible region was detected by detected reflected sound.
For example, in the Japanese Unexamined Patent Publication (KOKAI) No. 3-159400, there is disclosure of technology for an ultra-directional speaker system which uses a speech signal and ultrasonic waves and which provides high directionality. More specifically, an ultrasonic signal of a prescribed frequency is used as a carrier wave, this being amplitude modulated by a speech signal, the resulting modulated signal being output via an ultrasonic vibration element.
In the above-noted patent publication, there is further noted in that acoustic vibration that is output from the speaker and reflected from a listener is detected and the sound source is switched.
FIG. 5 and FIG. 7 illustrate the principle of an ultra-directional speaker system according to the prior art.
As shown in FIG. 7, this has a speech generation means 101, an ultrasonic generation means 120, an amplitude modulation means 131 that is connected to the speech generation means 101 and the ultrasonic generation means 120, an electro-acoustic transducer means 104 which converts an ultrasonic modulated signal that is output by the amplitude modulation means 131, if desired passed through an amplification means 132, to an acoustic signal, and wherein the ultrasonic modulated signal that is output from the electro-acoustic transducer means 104 striking a listener 105 and being reflected, this reflection wave being detected by the acoustic detector 121, the controller 122 switching the input signal switch 123 in accordance with whether or not there is a listener in an audible range, a selection being made thereby of the input signal from either speech generator (A) 111 or the speech generator (B) 112.
By doing the above, the required information is only passed in the case in which there is a listener 105, and in the case in which there is no listener, it is possible, for example, to play background music.
In the Institute of Electronics and Communications Engineers Technical Report EA-94-37 (1994-08, pp. 25-30, xe2x80x9cSpatial Sound Source Using a Parametric Array Beamxe2x80x9d), there is indicated the use of a reflector to cause collected reflection of an acoustic vibration, thereby creating a virtual sound source.
That is, as shown in FIG. 8, which illustrates the configuration of the above-noted technology, this system comprising an ultra-directional speaker system 1 that has a speech generation means 10, an ultrasonic generation means 20, and an amplitude modulation means 30 that is connected to speech generation means 10 and the ultrasonic generation means 20, and an electro-acoustic transducer means 50 that converts an ultrasonic modulated signal that is output by the amplitude modulation means 30 to an acoustic signal, if desired passing through an amplifier means 40, and in that the ultrasonic modulated signal output from this ultra-directional speaker system 1 causes the acoustic vibration to be reflected and collected by the acoustic reflector 2, so that it strikes a listener as a virtual sound source that is positioned in front of the listener.
In the above-noted prior art ultra-directional speaker system, as shown in FIG. 5, the carrier used is an ultrasonic signal, that is, a high-frequency signal that is modulated by an appropriate speech signal that it the transmitted signal, this modulated signal being generated by amplitude modulation, and being output by the above-noted electro-acoustic transducer means.
The ultrasonic modulated signal is subject to distortion as it propagates through the air, and the envelope thereof is demodulated to restore it to its original form, enabling it to be heard as actual speech.
In addition to the above, in the Japanese Unexamined Patent Publication (KOKAI) No. 1-309500, there is disclosure of a technology whereby ultrasonic waves are caused to oscillate in an ultrasonic oscillator, verification being made by the speaker system as to the location of a listener, whereupon an optimum acoustic environment is formed at the location of the listener, with the acoustic signals that are output from a plurality of speaker systems are adjusted. There is in this publication, however, no disclosure of the use of an ultra-directional speaker system.
Additionally, in the Japanese Unexamined Patent Publication (KOKAI) No. 6-233397 as well, there is indicated an adjustment made in the same manner so as to form an optimum acoustic environment at the location of a listener, although this is also lacking a disclosure of the use of an ultra-directional speaker system.
In the above-noted prior art system as cited from the Japanese Unexamined Patent Application publication H3-159400, the following problems existed.
Specifically, the first problem is that it is not possible to maintain the acoustic output from the electro-acoustic transducer at all times at the optimum sound level.
The second problem is that, because the sound source is always fixed, the way the listener hears the sound will depend upon the distance with respect to the listener.
Even if the acoustic vibration is the same, if the sound source is at a distance of 1 meter it will be heard as sounding like it is at a distance of 1 meter away, and if it is at a distance of 1.5 meters, it will be heard as sounding like it is at a distance of 1.5 meters away, the respectively effects being different.
The reason for this is that because the information obtained from the acoustic detector is only whether or not a listener exists, it is not possible to know how far away the listener is.
For this reason, in prior art technology which used an ultra-directional speaker system, an attendant problem was that it was impossible to create the optimum acoustic environment from the standpoint of the listener at the position the listener occupies.
Accordingly, an object of the present invention is to provide an improvement over the above-noted problems which accompanied the prior art, by providing an ultra-directional speaker system that is capable of creating for a listener an ideal acoustic environment, without greatly changing the circuit configuration from that of the past, and without an increase in cost, and also to provide a method of driving such a speaker system.
Additionally, using an ultra-directional speaker system according to the present invention it is possible to provide a speaker system that performs automatic positioning.
To achieve the above-noted object, the present invention has the following basic technical constitution.
Specifically, the first aspect of the present invention is an ultra-direction speaker system that has a speech generation means, an ultrasonic generation means, an amplitude modulation means to which the speech generation means and the ultrasonic generation means are connected, an electro-acoustic transducer means that converts an ultrasonic signal that is output from the amplitude modulation means to an acoustic signal, and a virtual sound source setting means that detects a reflection wave from a listener of the ultrasonic wave that is output from the electro-acoustic transducer means and sets the position of a virtual sound source.
A second aspect of the present invention is a method for driving an ultra-direction speaker system that has a speech generation means, an ultrasonic generation means, an amplitude modulation means to which the speech generation means and the ultrasonic generation means are connected, an electro-acoustic transducer means that converts an ultrasonic signal that is output from the amplitude modulation means to an acoustic signal, and a virtual sound source setting means that detects a reflection from a listener of the ultrasonic wave that is output from the electro-acoustic transducer means and sets the position of a virtual sound source, whereby the position of a listener is detected from a reflection from the listener of the ultrasonic modulated wave that is output from the electro-acoustic transducer means, and the curve rate of an acoustic reflector is adjusted accordingly.
By adopting the above-noted technical constitutions, an ultra-directional speaker system and speaker system drive method according to the present invention, even if the listener moves, it is possible for the listener to hear sound that is from the same apparent position.
And thus, wherever the listener stays, he can perceive the sound from a sound source which is located at the most suitable place to listen it and further he can always listen the sound with the maximum sound pressure as large as possible.
In the present invention, that is, an automatic-positioning speaker system is provided, and in an automatic-positioning speaker system that makes used of the above-noted ultra-directional speakers, the distance with respect to a listener is calculated from a reflection from the listener of an acoustic wave that is radiated from an electro-acoustic transducer, the position of a vertical sound source being changed in accordance with this distance, so that the listener senses the virtual sound source as coming from a fixed position.